Making calcium aluminate sinter



Patented Get. 26, 1948 MAKING CALCIUM ALUMINATE sin'rnn Kelly L. Elmore, near Sheffield. Ala; assignor to Tennessee Valley Authority, a corporation of the United States No Drawing. Application August 17, 1944, Serial No. 549,944

(Granted under the act of March 3,1883, as amended April 30, 1928; 370 0. G. 757) 4 Claims.

The invention herein described may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

. 2 of at least one of the principal end components of the sinter at equilibrium, and sintering the mixture so prepared.

In the conversion of the relatively insoluble alu- This invention relates to the recovery of alu- 5 mina contained in high silica aluminiferous mamina from raw materials containing aluminum terial, limestone or other calcium oxide containcompounds, particularly relatively low-grade 'aluing a reagent is mixed with the material to prominiierous material containing a relatively high duce a predetermined ratio of A1203, CaQ, and proportion of silica. S102 in the sinter as required for the specific It has been proposed to produce alumina from process employed. It is considered that the pro high silica raw material by many methods includportions of the constituents of the mixture are ingthe sintering of such material with the proper such as to produce in the sintered product siliproportion of limestone to produce calcium alucates and aluminates predominately 2Ca0.SiOz, minates from which the alumina is subsequently SCaOfiAlzOs. and CaO.Al2Oa. When a charge of extracted and the alumina precipitated from the the raw material and reagent is subjected to heat extract. Some of the proposals are directed to treatment, it is preferable to sinter rather than the ratio of alumina, silica and calcium oxide fuse in order that the products fromthe' heat which shall be present in a mixture to produce a treatment may have the alumina more readily sinter of highest extractable alumina. extracted therefrom. If such a charge were fused The principal object of the present invention is all of the constituents thereof would not only be to provide a method for the more rapid acceleraassociated with each other at a much higher temti-on of the conversion of the relatively insoluble perature which would in itself accelerate the realumina in the raw material to soluble material actions involved, but they.woulda1so be in more in a sinter. Another object of this invention is intimate contact, thereby hastening the reaction to provide a methodfor the acceleration of the to form the ultimate products resulting from the conversion of alumina into a soluble form using heat treatment. However, when the charge is presently known methods insofar as the basic mamerely sintered, a considerable time is required terials used for such conversion are concerned. to produce the ultimate products even though the Other objects of this invention include the proconstituentsof the charge are intimately mixed vision of a method for economically accelerating 3 before and during the passage through the heatthe conversion of alumina in high silica raw maing zone. terial which will reduce the time for treatment In the present invention a small proportion of of such material during sintering with a consematerial having a crystal structure and chemical quent increase incapacity of sintering apparatus. composition of at least one of the p i pal The present invention is directed to a process components of the sinter at equilibrium is added of making a, calcium sinter from finely divided to the mixture of normal constituents of the aluminum ore and limestone whereby the alumina charge before the sintering operation. The content of the ore is more readily rendered soluchemical components and crystallographic charble in dilute sodium carbonate solutions by mixacteristics of such principal end components ing intimately with the finely divided ore and 40 taken from E. S. Shepherd and G. A. Rankin, Ind. limestone a. small proportion of a material hav- Eng. Chem. 3, 21127 (1911), are shown in Taing a crystal structure and chemical composition ble 1.

Table I Compound Index ofrelraction Crystal system Other Characteristics Above14l0 a=l.7l4,fl=l.720, 1131 Optically positiv GAO-A1203 orthorhombic A series of examples are given to show the conversion of alumina in Ross clay with the following percentage composition: A1203, 38.50; CaO, 0.68; S102, 43.34; TiOz, 2.42; F6203, 0.68; ign. loss. 18.43 when sintered with Hook's limestone with the following percentage composition: CaO, 55.5; SlOz, 0.17;, MgO, 0.51; R203, 0.33; ign. loss, 4-3.4, in the proportion of 33% by weight of clay and 67% by weight of limestone; In order to make a more accurate representation of the influence of the added small proportionof. one of, the principal end components, it was necessary to hold the mixtures at sintering temperature fora relatively short-time interval so thatthe rate of reaction could be judged by the percentage of alumina made soluble in the limited time. below is shown the effect of various additions of synthetically prepared compounds to clay-limestone mixtures on the percentage of aluminamade soluble by sintering the mixtures for, aperiod of five minutes at 1390 C.

Table II A'mount Increase in Scl- Alumina Solu- Material added Added bility, Percent Y,PT-

cent of of to? 1 A cent of total Mixture 12 a A1203,

None'(contr0l) 23 CaOA 0 1 37v 14 CaQAhOz" 2 39 16 soaocnnoa 1 35 12 aca emics" 2 as 15 zc'aosi 1 41 18 2Ca0zsi0 2 s5 12.

- The data in. the precedingltable show that the processor therpresent'invention, wherein a small proportion of thematerial'having: a crystal structure: and. chemical composition of at least one of the principal end components of the sinter at equilibrium increases the percent of extractable alumina by from. 52% to 78 under the conditions which such data. were obtained.

Theitime' of treatment in. semi-plant or plantscale' operation may extend for a period of thirtyrto ninety'minutes with a temperature of 1370 C31. Hie-time required" for conversion of the alumina in; the charge: to an extractable form by the: addition: of 1% of the added material of the present-invention. was reduced to ten minutes whichris at leastone-third or that requiredwithout the addition of added material, and the percentage of extractable: alumina was increased from; 7 0% to 83%. which is an increase of 18%.

It will be seen, therefore, that this invention actually: may be carriedoutbythe use of various modifications. and: changes without departing from its-spiritand scope:

1. rocessofmaking a. calcium aluminate sin-- In Table II.

ter from finely divided, highly siliceous alumi num ore and limestone whereby the alumina content of the ore is more readily rendered soluble in dilute sodium carbonate solution, which comprises (a) mixing intimately with the finely divided ore and limestone a material having a crystal structure and chemical composition of at least one of the principal end components of the sinter at equilibrium, said admixed material being incorporated in an amount sufficient to substantiallyincreasethe solubility of the alumina in the mixture after sintering, and (b) sintering the mixture so prepared.

2; Process of making a calcium aluminate sinter-from finely divided, highly siliceous aluminum ore and limetsone whereby the alumina content of the ore is more readily rendered soluble in dilute sodium carbonate solutions, which comprises (a) mixing intimately with a finely divided ore and limestone about 1% to 2% of calcium alu minate with composition corresponding to the formula CaOAIzOs, and- (b) sintering the mixture so prepared.

3. Process of making a calcium aluminate sinter" from finely divided, highly siliceous aluminum ore and limestone whereby the alumina content of the ore is more readily rendered soluble indilute sodium carbonate solutions, which comprises (a) mixing intimately with the finely divided ore and limestone about 1% to 2% of calcium' aluminate with a composition corresponding to the formula 5CaO.3Al2O3, and (b) sinter-- ingthe-mixture so prepared.

4. Process of making a calcium alumina-ts sinter from finely divided, highly'siliceous-aluminum ore and limestone whereby the alumina content of the ore is more readily rendered soluble in dilute sodium carbonate solutions, which comprises (or) mixing intimately with the finely divided oreand limestone about 1% to 2% of calcium silicate with a composition corresponding to the formula ZCaQSiOz, and (b) sintering the mixtureso pre pared.

KELLY L. ELMORE'.

REFERENCES CPIED The f llowing references are of record in the. file ofthis patent UNITED STATES IE'AliENilFS Number Name Date 1,891,608 Scheidt Dec. 20, 1932. 2,141,132 Folges Dec. 20, 1938..

, FOREIGN PATENTS Number Country Date 17,356 Great Britain .1908 

